1. Technical Field
The present invention generally relates to fuel control systems and, more particularly, to a method of using fuel vapors from the fuel tank to power an engine during cold engine operation.
2. Discussion
Modern automotive vehicle engines commonly employ injected fuel for combustion. At start-up, when the engine is not fully warm, the injected fuel is commonly cold and in a liquid state. Cold fuel, which is not easily vaporized, is less combustible than warm fuel. As such, the liquid fuel poorly combusts at start-up. This may lead to poor emissions.
Attempts have been made before and after combustion to improve emissions quality. One pre-combustion treatment has been to heat the fuel prior to its injection. By heating the fuel, it becomes more easily vaporized thereby improving its combustibility. While successful, such pretreatment heating is complex and expensive to implement. A common post-combustion treatment involves the employment of a catalyst in the engine exhaust gas stream. The catalyst burns the undesirable exhaust gas constituents prior to their passage to the atmosphere. While also successful, such post-combustion treatment is still expensive and complex to implement.
Modern automotive vehicles are also commonly equipped with a fuel vapor purge control system. Fuel within the fuel tank tends to vaporize as temperatures increase. The vaporized fuel collects in the fuel tank and is periodically removed by the purge vapor control system. The fuel vapors from the tank are initially collected and stored in a canister. When the engine operating conditions are conducive to purging, a purge valve is opened thereby allowing the engine to draw the fuel vapors from the purge canister for combustion.
While such purge fuel vapor control systems are very efficient, some fuel vapor is commonly present in the dome portion of the fuel tank at start-up. Advantageously, it has now been discovered that this fuel vapor can be used for combustion during cold engine operation instead of the liquid fuel normally supplied from the fuel injectors.